Environmental contaminants are not always particularly cooperative when it comes to the sites they impact. Some sites can be quite complicated, particularly when the contamination gets into the bedrock which can require the use of novel remedial strategies.
One successful example of such an approach involved a site where trichloroethylene had been discharged from a storage tank into the subsurface, which consisted of fill underlain by saprolite, a very dense partially weathered rock. The plume covered approximately 15 acres with historical concentrations in the source area up to 250 mg/L of TCE with the mid-plume area displaying concentrations up to 96 mg/L. Site access was limited throughout much of the plume, with a steep slope near the source, a public roadway adjacent to the property, and a forest off-site. Groundwater moved through this rock as deep as 50 to 60 feet below ground surface and as shallow as 7 to 10 feet below. Groundwater seepage velocity was relatively slow at 60 feet per year.
Initial remediation efforts included the removal of the TCE storage tank, associated sumps, piping, and 140 tons of impacted material overlying the bedrock.
To treat the groundwater, a pilot-scale program was implemented using high-solid slurries (HSE) of Remox S-B (permanganate, sand blend) and zero valent iron (ZVI). Slurry emplacement is a technique where a fluid is introduced at a pressure that can overcome the confining stress and material strength of the solid matrix and induce or enhance fluid flow into the formation. This resulting contrast in hydraulic conductivity between the emplaced ZVI and permanganate within the formation will result in a deflection of groundwater flow into the more permeable treatment zone.
Both the Remox S-B and the ZVI were chosen because they both can destroy unsaturated chlorinated solvents such as TCE without generating hazardous intermediates or breakdown products, their long life spans (several months to a year for Remox and up to decades for ZVI) and, in the case of Remox, its ability to chemically diffuse into fine grained soil and bedrock.
In the source area, two 4” borings were sonically drilled, and approximately 29,000 lbs of Remox S-B was emplaced. Five similar borings were drilled at the downgradient edge of the plume, and approximately 73 tons of ZVI were emplaced.
Post-treatment sampling events indicated TCE destruction in the targeted source and downgradient areas. Permanganate was observed in 11 of the 15 monitoring locations within the source area, with significant TCE reductions ranging from 84 to 100% compared to baseline concentrations. One monitoring well within the source was reduced from 82,000 ug/L to non-detect.
TCE in the monitoring wells downgradient of the ZVI barrier showed reductions from 46-100%.
Based on these positive results, there are plans in place for a full scale treatment program. It was an effective demonstration of how a novel approach can achieve successful remediation even on a complicated site.
Both Remox S-B and ZVI are available from CCC upon request. CCC is also a distributor for the other products in Carus’ line of remediation-grade permanganates, Remox-S (potassium permanganate) and Remox-L (sodium permanganate).